Containers of pressurized fluid are ubiquitous in a modern society and include, for example, jugs of refrigerant for charging refrigeration systems and tanks of propane for heating. Such containers typically are charged under pressure using a filling system. A conventional filling system comprises a central tank for storing the fluid, conduit for connecting the central tank to one or more filling stations, one or more pumps to motivate fluid flow toward the fill station(s), and typically a programmable controller for controlling the filling system's operation. A conventional filling system tends to be a specialized apparatus, and, as such, tends to represent a significant capital expenditure. Therefore, to maximize its utility, a filling system usually is configured to accommodate a number of fill stations, thereby increasing the number of containers that can be filled at a given time. To this end, the conduit usually comprises a common section from which a number of leader sections extend, each leader section supplying a particular fill station. In operation, the filling system initially pulls a vacuum to evacuate residual fluids, impurities and/or air from each container connected to a fill station. Once the containers have been evacuated, the system transfers fluid from the central tank to the individual containers at relatively high pressure, for example, usually between 50 psi and 2000 psi.
Aside from the fluid, it is often preferable to introduce one or more additives to the container. As used herein, an "additive" is any substance that is added to the container to render the fluid detectable to the senses, to improve the performance of the fluid, or to improve performance of apparatus using the fluid. Such additives are well known in the art. For example, dyes may be added to refrigerants and other fluids used in circulating systems to provide operators with a visual indication of a leak so as to avoid an unnecessary atmospheric release of the fluid and to keep the system operational. In situations where the fluid is explosive or toxic and the early detection of a leak thereof is critical to minimizing danger, an odor agent such as a mercaptan can be added to the container. It also may be preferable to add oil or other lubricants to fluids used in machinery having wearing components such as refrigeration units.
One approach to introducing an additive to a pressurizable container is to mix it in the central tank of a filling system and then use the filling system to distribute the fluid/additive mixture through the conduit to the various containers. Such an approach is appealing because it uses the existing filling system to pump the additives to all the containers. Additionally, it allows the additives to be mixed with the fluid in bulk fashion and distributed among the individual containers during the course of ordinary filling. Unfortunately, although efficient, this approach tends to contaminate the filling system with the additives. This is particularly problematic since a common filling system usually is employed to fill containers with a variety of different fluids, some of which not only do not require such additives, but are compromised by such additives. For example, it is generally preferred that fluids such as alcohol, kerosene, and water remain crystal clear so as to ensure their purity. Color in the fluid may serve to mask or suggest an impurity.
Another approach to introduce additives in pressurizable containers is to have a dedicated fill station for a particular fluid and a combination of additives. Although this takes advantage of a centralized facility for injecting additives and avoids the problem of contamination mentioned above, the expense of a dedicated system is prohibitive and renders such an approach impractical. Also, seasonal products, such as refrigerants and propane tanks, are commonly filled during "campaigns," in which many cylinders are filled in a relatively short time span, thus necessitating many filling stations.
Therefore, a need exists for a system and method of supplying additives to a pressurizable container that can be used with an existing system, but which avoids contaminating the filling system. The present invention fulfills this need among others.